Involvement of photoinhibition and redox balance in acclimation and developmental processes of plants

Abstract

Environmental constraints and developmental processes in plants can lead to light energy excess in chloroplasts by lowering the threshold at which light becomes saturating by a lack of electron acceptors in the light-processing structures. Inactivation of photosystems due to high energy quanta is generally known as photoinhibition, a process that can compromise growth and organ development in plants due to an imbalance of the cellular redox state that leads to enhanced oxidative stress. Hence, it is essential to determine environmental factors and stages of organ development that influence the extent of photoinhibition and mechanisms triggered to avoid photoinhibition and cope with photo-oxidative stress, so that plant survival is not put in jeopardy. For this reason, leaves from an ecologically important Mediterranean plant, flowers from a relevant commercial crop and fruits from a highly appreciated agronomic tree, were selected to analyse events leading to photoinhibition and strategies to allow plant acclimation and correct organ development. With this regard, mastic trees were selected to study their sensitivity to cold stress during Mediterranean winters and altitudinal distribution, to determine if antioxidant strategies and leaf phenology influence their ability to survive environmental constraints. On the other hand, lily flowers were selected to study photoinhibitory events taking place during flower opening and how phytohormones could regulate the timing of flower opening by interacting with photo-oxidative stress signals. Besides, sweet cherry fruits were also selected to better understand physiological events related to ripening onset and chloroplast dismantling with the production of antioxidants and hormonal signals involved. Our results show that timing and stage of organ development directly condition the outcomes of photoinhibition with regards of chloroplast status and antioxidants produced, with a general prevailing mechanism where reduced Fv/Fm triggers higher lipid peroxidation and parallel production of phytohormones and antioxidants that deal with increased photo-oxidative stress. In conclusion, photoinhibition does not compromise plant or organ survival, but prompt the activation of signalling networks that promote metabolic changes to fine-tune the timing and severity of this process to allow acclimation and correct organ development.